To improve the performance and, particularly, speed of an electronic circuit system constituted by a plurality of semiconductor chips, it has become increasingly important to reduce the length of the interconnections between the semiconductor chips to a minimum.
For this purpose, a technique of minimizing the interconnections between a plurality of semiconductor chips by stacking them has been studied instead of the conventional method of mounting a plurality of semiconductor chips two-dimensionally on a multilayer board. Such a semiconductor device formed by stacking a plurality of semiconductor chips is called a multichip module.
In addition, with the use of a multichip module of this type, different types of semiconductor chips manufactured by different processes can be stacked on each other into one hybrid semiconductor device.
To manufacture a multichip module, vertically stacked semiconductor chips must be electrically connected. For the realization of such connection, the present inventors have already proposed the use of connection plugs (chip-through plugs) that extend through vertically stacked semiconductor chips to connect them (Japanese Patent Application No. 9-305784).
A paste according to the present invention is characterized by containing solids having a conductive substance and a resin, and a solvent for dissolving the resin, wherein a solids content is not less than 60 vol %.
In the present invention, the solids content indicates the ratio of solids (e.g., metals, glass, and resins) in a paste, which are left on a substrate upon hardening the paste to the total paste (solids+solvent). In the following description, this ratio indicates the volume ratio unless otherwise specified.
In the present invention, the solids content of a paste is set to 60 vol % or more for the following reason. When a paste is hardened (dried) after it is buried in a trench with a squeegee, the solvent in the paste volatilizes.
Upon this volatilization of the solvent, the volume of the paste reduces. If the volume reduction of the paste is large, the trench cannot be filled with the paste. A deterioration in buried shape due to such a volume reduction can be effectively prevented by increasing the solids content of the paste.
When the solids content is set to 60 vol % or more as in the present invention, in particular, occurrence of a volume reduction that causes connection failures and the like can be effectively prevented, and the trench can be filled with the paste with a good buried shape.
In addition, another paste according to the present invention is characterized by containing solids having a conductive substance and a resin, and a solvent for dissolving the resin, wherein a viscosity ratio is not more than 2.
In the present invention, the viscosity ratio of a paste indicates the ratio of viscosity changes in a case wherein the viscosity of the paste is measured with a rotational viscometer at rotational speeds that differ by one order of magnitude.
Assume that the viscosity of a given paste is measured with the rotational viscometer at different rotational speeds, and viscosities of 200 Paxc2x7s and 100 Paxc2x7s are respectively measured at 10 rpm and 100 rpm. In this case, the viscosity ratio is 200 Paxc2x7s/100 Paxc2x7s =2. The burying ratio of a viahole is the ratio of the paste to the sectional area of the viahole when the cross-section of the viahole is observed after a paste burial test.
In the present invention, the viscosity ratio of a paste is set to 2 or less for the following reason. When the viscosity ratio is high, the viscosity of the paste receiving force from the squeegee becomes low. When the paste receives no force, the viscosity increases. For this reason, when the paste is buried in a trench with the squeegee, the viscosity of the paste becomes high at the bottom portion of the trench. This makes it difficult to bury the paste.
If, however, the viscosity ratio is set to 2 or less as in the present invention, an increase in the viscosity of the paste at the bottom portion of the trench can be effectively suppressed. This prevents formation of voids that cause a connection failure and an increase in resistance. Hence, the trench can be filled with the paste.
Furthermore, still another paste according to the present invention is characterized by containing solids having a conductive substance and a resin, and a solvent for dissolving the resin, wherein a solids content is not less than 60 vol % and a viscosity ratio is not more than 2.
The trench can be filled with this paste with a good buried shape.
In consideration of the buried shape, the viscosity of the above paste is preferably 200 pas or less. In addition, if the paste is to be used for a connection plug, the main component of the paste should be a conductive substance.
A connection plug according to the present invention is a connection plug made of a paste containing powder particles having different average sizes and buried in a connection hole. This connection plug is characterized in that the paste contains 10% or more of a powder having an average particle size of 3 xcexcm or more.
In this case, the paste preferably contains 10% or more of a powder having an average particle size of 1 xcexcm or more. The powder may be the main component of the paste or another component. For example, the connection hole is a through hole extending through a semiconductor chip.
The viscosity of the paste is determined by the total surface area of powder particles in the resin contained in the paste. As the total surface area increases, the viscosity decreases. With the use of a connection plug containing a powder of a large average particle size as in the present invention, therefore, the paste as the connection plug can be buried in a trench with a good buried shape. In addition, according to the study conducted by the present inventors, it was found that the occurrence rate of cracks could be reduced sufficiently by setting the content of such a powder to 10% or more.
A burying method according to the present invention is characterized in that a paste according to the present invention is buried in a trench formed in the surface of a substrate.
With this arrangement, a good buried shape can be realized even by a burying method using a squeegee.
In addition, the burying method according to the present invention is characterized in that a powder dispersion is applied on a region including a trench formed in the surface of a substrate, and the powder is precipitated in the solution, thereby filling the trench with the powder.
According to this arrangement, since the trench is filled with the small-volume powder that precipitates, a deterioration in buried shape, e.g., formation of a void, is suppressed.
In this case, as the above dispersion, a solution to which a resin is added is preferably used. With the use of such a solution, the powder particles can be temporarily fixed with the resin.
In addition, the powder preferably partially contains glass. With the use of this powder, the glass melts in a calcination process to fill the trench without any recess.
A method of manufacturing a semiconductor device according to the present invention is characterized by comprising the steps of forming a trench in a surface of a substrate, filling the trench with a calcination type paste formed inside and outside the trench, temporarily hardening the paste, removing an excess portion of the paste outside the trench, and calcining the paste.
In the present invention, the excess portion of the paste is removed in the step of temporarily hardening the paste, in which the paste can be easily removed, instead of the step after calcination in which the paste is difficult to remove. Even if, therefore, the width of the trench increases, and the amount of paste increases, an excess paste portion can be removed without taking much time.
According to the present invention, therefore, even if the width of the trench is increased to decrease the resistance of the connection plug, an increase in the formation time of a connection plug made of a paste can be suppressed.
Preferred aspects or more detailed forms of the semiconductor device manufacturing method according to the present invention will be described below.
(1) The excess portion of the paste outside the trench is removed by polishing or etching. The above polishing is preferably CMP (Chemical Mechanical Polishing). The above etching is RIE (Reactive Ion Etching) or CDE (Chemical Dry Etching).
(2) After the paste is calcined, the lower surface of the substrate is removed until the paste appears, thereby forming a connection plug made of the paste penetrating the substrate. More specifically, the lower surface is removed by polishing or etching. The above polishing is preferably CMP. The above etching is RIE or CDE.
In cases (1) and (2), after the trench is filled with the paste to a certain degree, different pressures are applied to portions inside and outside the trench, thereby filing an unfilled region in the trench with the paste. Even if the depth of the trench increases, the overall trench can be filled with the paste. In these cases, therefore, even if the depth of the trench is increased to decrease the resistance of a connection plug, a connection plug made of a paste without any void can be formed.
(3) After the step of calcining the paste, an interconnection is formed on the paste.
(4) This method is characterized by using a conductive paste (plug body) as the above paste.
In cases (3) and (4), an insulating film is formed in advance between the surface of the trench and the conductive paste. If, however, an insulating substrate such as a ceramic substrate is used as the above substrate, such an insulating film is not required. Furthermore, if an insulating paste is used as the above paste, a conductive film (connection plug body) is formed in advance on the surface of the trench.
In addition, another semiconductor device manufacturing method according to the present invention is characterized by comprising the steps of forming a trench in a major surface of a substrate, burying a calcination type paste in the trench so as to fill a space including at least a portion on a bottom surface of the trench, filling an unfilled region in the trench with the paste by making a pressure on the paste outside the trench higher than a pressure on the unfilled region in the trench filled with the paste, and removing an excess portion of the paste outside the trench.
Furthermore, still another semiconductor device manufacturing method according to the present invention is characterized by comprising the steps forming a trench in a major surface of a substrate, burying a calcination type paste in the trench so as to leave a space including at least a portion of a bottom surface of the trench, filling an unfilled region in the trench with the paste by making a pressure on the paste outside the trench higher than a pressure on the unfilled region in the trench filled with the paste, temporarily hardening the paste, removing an excess portion of the paste outside the trench, and calcining the paste.
According to the present invention, even if the width and depth of a trench are increased to sufficiently decrease the resistance of a connection plug, an increase in the formation time of a connection plug made of a paste can be suppressed, and a connection plug made of a paste without any void can be formed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.